12-Foot Free-Flight Tunnel under construction: The free-flight wind tunnel is a steel sphere 60 feet in diameter and can be supplied with air compressed up to two or more atmospheres in which the operators will work. A decompression chamber is provided so that the operators can return gradually to normal atmospheric pressure. The tunnel itself, which is mounted on a steel framework inside the sphere, has a test section diameter of 12 feet and is about 30 feet long. The drive consists of a 600-horsepower electric motor turning a 15-1/2 foot diameter propeller. The whole apparatus is mounted on bearings so that the tunnel can be tilted through a wide range of angles to correspond to the angle of glide of the model airplane.